An RFID (Radio Frequency IDentification) system that is becoming popular in recent years is employed for article management, such as inventory management, which uses RF tags attached to articles to be managed.
PTLs 1 to 4 disclose examples of such an RFID system. With the techniques disclosed in PTLs 1 to 3, RF tags are attached to articles to be managed. The articles to be managed are managed by determining that an article to be managed is present if the tag information of an RF tag is readable and that no article to be managed is present if the tag information is unreadable. Unfortunately, the practical application of such an RFID system poses the following problems.
The first problem is unauthorized reading of the tag information of RF tags. When, for example, the RFID system is used to manage commodities lined up on the shelves of retail stores, a third party different from consumers who will purchase the commodities or salesclerks who are engaged in commodity management can also read the tag information of RF tags attached to the commodities. In such a case, for example, a consumer who will purchase or has purchased a commodity can be associated with the information of the commodity, leading to violation of his or her privacy. When the RFID system is similarly used to manage products to be shipped or raw materials stored in warehouses, information security concerns are encountered as well. That is, a third party can know whether raw materials or products equipped with RF tags have been warehoused/shipped, by reading the tag information of the RF tags.
The second problem is the high cost of RF tags. Nowadays, the cost per tag in the UHF (Ultra High Frequency) band has lowered to about less than ¥10, which is still higher by about two orders of magnitude than, for example, the cost of barcodes similarly used for article management, especially commodity management. Therefore, in terms of cost performance, it is difficult to attach RF tags to articles that cost approximately ¥1,000 or less.
PTL 5 discloses a technique for tackling such problems. PTL 5 relates to a technique for managing articles, like the method for using the above-mentioned RFID system. More particularly, PTL 5 relates to a smart shelf that uses an RFID system and to a technique for monitoring the presence or absence of articles on the shelf.
In PTL 5, RF tags are placed on the shelf. Articles serving as objects for management (to be referred to as articles to be managed hereinafter) are positioned to prevent an RFID reader from reading a plurality of RF tags placed on the shelf. In other words, in PTL 5, articles to be managed are placed between the RF tags and an antenna that accompanies the RFID reader. In PTL 5, the quantity of articles is monitored in accordance with the following procedure.
(a) The RFID reader illuminates the shelf with electromagnetic radiation.
(b) The number of RF tags whose tag information cannot be read by the RFID reader because of the presence of the articles is measured.
(c) The quantity of articles is measured based on the information obtained in (b).
Note that the RF tags are tuned so that the articles prevent the reader from reading the tags when the articles are placed between the reader and the tags.
With the above-mentioned technique disclosed in PTL 5, when articles to be managed are placed between the RFID reader and the RF tags, that is, when articles to be managed are located on the shelf, the articles interrupt the line-of-sight vision of the RF tags and the RFID reader to prevent the RFID reader from reading the tag information of the RF tags. In other words, when articles to be managed are present, the tag information of RF tags corresponding to these articles is unreadable so that the presence of the articles to be managed can be detected. When no articles to be managed are located on the shelf, that is, when no articles to be managed are placed between the RFID reader and the RF tags, no articles to be managed interrupt the line-of-sight vision of the RF tags and the RFID reader so that the RFID reader can read the tag information of the RF tags. This means that when articles to be managed are absent, the tag information corresponding to these articles is readable so that the absence of the articles can be detected. It is, therefore, possible in PTL 5 to detect the presence or absence of articles and, in turn, to manage the articles on the shelf. The manageable articles are assumed to contain a metal, water, or other materials that interfere with the transmission of radio frequency energy.
With the above-mentioned technique according to PTL 5, since RF tags are not attached to the articles to be managed but remain on the shelf, neither violation of privacy nor information security concerns result from unauthorized reading of the tag information of the RF tags attached to the articles to be managed. With the technique according to PTL 5, the first problem, that is, unauthorized reading of the tag information of the RF tags by a third party does not occur. In addition, with the technique according to PTL 5, since RF tags are not attached to the articles but remain on the shelf, the RF tags can be repeatedly used and therefore involve a cost per article almost equal to the value of the tag divided by the number of times the tag is used. In other words, the technique according to PTL 5 can solve the second problem, that is, the high cost of the RF tags by sufficient repetitions of use.
PTLs 6 to 9 disclose techniques for non-contact signal communication that uses electromagnetic coupling. With these techniques, a coupler has its one end connected to its other end through electromagnetic capacitive or inductive coupling so that signals can be communicated even if the two ends of the coupler are physically separate from each other.